Cucumber is ready to run in OSGi containers

I have produced 2 commits that allow to run cucumber in OSGi containers.

* The first one adds OSGi headers to core, java and JUnit bundles.
* The second changes the loading of the USAGE.txt in RuntimeOptions, because due to OSGi class loading cause problems. I wrote more details in the commit message.

*NOTE*: Please release cucumber-jvm-deps with my other pull request (see https://github.com/cucumber/cucumber-jvm-deps/pull/3), because this changes make only sense when the jvm-deps bundle has also OSGi headers.

Thank you!